Filler materials are added to certain other materials, in particular building materials, in order to obtain or improve the following characteristics, namely: the mechanical abrasion strength and/or heat-resistance, and particularly fire-resistance and/or resistance to temperature changes, and/or thermal insulation and/or sound insulation and/or the electrical insulation properties and/or the workability of masses, mixtures or compositions, particularly building compositions, and/or paints and the like. For the purpose of improving the above-listed properties, it is customary to use, e.g., asbestos fibre, mineral wool, glass wool, pearlites, vermiculties, fragmented pumice stone, refractory clay, powdered refractory clay, slag-sand, quartz sand, sintered corundum, sintered dolomite, alumina, powdered dolomite, gypsum, sawdust, powdered cork and other materials. However, these materials fulfill the above-listed requirements only in part, or only imperfectly, or they raise problems in the production or processability of the materials. In addition, some of these materials are expensive or scarce, and others, such as asbestos, present considerable health risks which make their use undesirable.
On the other hand, various chemical-technical processes and production methods produce dust-like or powdered by-products which are not returnable into the processing cycle and for which no useful purpose was previously found. The disposal of such by-products may cause considerable expense because they must be deposited at authorized dumping grounds. This applies especially to dust-fine particles from emissions occuring in the production of silicon or ferrosilicon which, because of their low density and correspondingly-large volume, take up much space. In addition, such materials, have to be carefully piled up or comglomerated into larger and more manageable lumps by expensive processing.